merge: extract method for checking for conflicting untracked file Now that the functionality is collected in one place, let's extract it to a method.

merge: create 'cm' action for 'get or merge' case We still have one case of a call to _checkunknownfile() in manifestmerge(): when force=True and branchmerge=True and the remote side has a file that the local side doesn't. This combination of arguments is used by 'hg merge --force', but also by rebase and unshelve. In this scenario, we try to create the file from the contents from the remote, but if there is already a local untracked file in place, we merge it instead.

merge: don't overwrite untracked file at directory rename target When a directory was renamed and a new untracked file was added in the new directory and the remote directory added a file by the same name in the old directory, the local untracked file gets overwritten, as demonstrated by the broken test case in test-rename-dir-merge. Fix by checking for unknown files for 'dg' actions too. Since _checkunknownfile() currently expects the same filename in both contexts, we need to add a new parameter for the remote filename to it.

merge: remove constant tuple element from 'aborts' The second element of the tuples in the 'aborts' list is always 'ud', so let's remove it.

merge: collect checking for unknown files at end of manifestmerge() The 'c' and 'dc' actions include creating a file on disk and we need to check that no conflicting file exists unless force=True. Move two of the calls to _checkunknownfile() to a single place at the end of manifestmerge(). This removes some of the reading of filelogs from the heart of manifestmerge() and collects it in one place close to where its output (entries in the 'aborts' list) is used. Note that this removes the unnecessary call to _checkunknownfile() when force=True in one of the code paths.

merge: introduce 'c' action like 'g', but with additional safety _checkunknownfile() reads the filelog of the remote side's file. For narrow clones, the filelog will not exist for all files and we need a way to avoid reading them. While it would be easier for the narrow extension to just override _checkunknownfile() and make it ignore files outside the narrow clone, it seems cleaner to have manifestmerge() not care about filelogs (considering its name). In order to move the calls to _checkunknownfile() out, we need to be able to tell in which cases we should check for unknown files. Let's start by introducing a new action distinct from 'g' for this purpose. Specifically, the new action will be just like 'g' except that it will check that for conflicting unknown files first. For now, just add the new action type and convert it to 'g'.